1. Field Of The Invention
The present invention relates generally to electrodeless light sources and, more particularly, to a method and apparatus for dimming an electrodeless fluorescent light source.
2. Background Of The Related Art
This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Conventional fluorescent lamps are driven with an electronic ballast which powers the lamps via electrodes disposed at each end of the lamp. The electrodes, however, are major life-limiting components of the fluorescent lamp. Electrodeless fluorescent lamps also are known. An electrodeless lamp is configured as a closed loop tube around which one or more coupling transformers are positioned. As with conventional fluorescent tubes, the electrodeless lamp is energized by an electronic ballast. However, rather than applying power to electrodes disposed at each end of a lamp tube, the ballast drives the coupling transformers, which, in turn, inductively couple the power to the lamp. The elimination of electrodes from the fluorescent lamp is particularly advantageous as it increases the life and reliability of the lamp and systems incorporating such lamps. Thus, electrodeless lamps are particularly useful in applications in which access to the lamps is restricted such that replacement of the lamps becomes difficult or expensive.
Backlit video display devices are one type of application in which the access to the lamp is not readily available. Such video displays may be found in computer systems, automatic teller machines, information kiosks, gas pumps, shipboard controls, etc. To enhance viewing of displayed images, such video displays commonly include a backlight source to provide a brightly lit background that contrasts with the displayed image. However, such video displays often are located in environments in which the ambient lighting conditions vary considerably, interfering with vivid viewing of the displayed image. For example, in a dimly lit environment (e.g., a cloudy day, the enclosed interior of a ship, etc.), a brightly lit background provides for the best viewing of a displayed image. However, in a brightly lit environment (e.g., a sunny day, a well-lit office, etc.), a dimly lit background provides for better viewing. Accordingly, it would be desirable to provide the capability to control the brightness of the backlighting to compensate for variations in ambient lighting to enhance the viewing capabilities of the video display unit further. Unfortunately, electrodeless lamps rarely are used in such displays due to the lack of suitable means for dimming such lamps.
The use of electrodeless fluorescent lamps is not limited to backlight sources for video display units or applications in which the lamp is not readily accessible. Electrodeless lamps also may be used in other types of applications requiring a light source, such as office or home lighting systems, desk lamps, etc. Moreover, if the control of the brightness of the light generated by the lamps in these other applications also is desirable, it would be advantageous to provide the capability to vary the brightness of the generated light in any type of lighting application in which an electrodeless fluorescent lamp is incorporated. Still further, it would be advantageous to provide a dimming module for electrodeless lamps that can be easily installed in existing electrodeless lighting systems to retrofit such systems with a brightness control capability
The present invention may address one or more of the problems set forth above.